The effect on ash deposition by blending high-calcium Zhundong coal with vermiculite: Focusing on minerals transformations

To solve the ash deposition problem caused by burning high-calcium Zhundong coal (ZDC), the addition of vermiculite is a promising solution. However, complete mechanisms of vermiculite addition reducing ash deposition are still unknown. In this paper, the effect of vermiculite on sodium emission, ash fusion characteristics, and mineral transformation is investigated. The results show that although vermiculite, with limited Na capture capacity, lowers the ash fusion temperatures (AFTs), it can greatly reduce ash deposition. In the combustion of ZDC, calcium-bearing minerals will react with clay minerals and then convert to molten glassy phase. Those molten minerals will take high melting point minerals, Ca(2)Al(2)SiO(7)and CaMgSi2O6, as bone, showing slagging phenomenon with high AFTs. When vermiculite is introduced, the main reaction products are Ca(2)MgSi(2)O(7)and Mg(2)SiO(4)and that reduces the extent of molten minerals formation. The main ash product transforming from Ca(2)Al(2)SiO(7)to Ca(2)MgSi(2)O(7)leads to the decrease of AFTs. The initial ash deposition with Ca(2)Al(2)SiO(7)still happens; however, vermiculite addition makes it hard for ash to grow on the existing ash deposit. The results of FactSage software agree with the experimental ones, and the proportion of slag decreases by 36% with vermiculite at 1250 degrees C.